Effective Diaphragm Area Test Program for Air Operated Valve Actuators

Transcription

1 Proceedings of the ASME/NRC th Pump and Valve Symposium PVS2017 July 17-18, 2017, Silver Spring, Maryland PVS Effective Diaphragm Area Test Program for Air Operated Valve Actuators Zachary Leutwyler Kalsi Engineering, Inc. 745 Park Two Drive Sugar Land, TX Manmohan Kalsi Kalsi Engineering, Inc. 745 Park Two Drive Sugar Land, TX Laurie Luckhardt GE Oil & Gas Canada, Inc. 133 King Street West PO Box Dundas, Ontario, L9H 6Y6 Lisa Thidavanh Kalsi Engineering, Inc. 745 Park Two Drive Sugar Land, TX Thomas Cunningham GE Oil & Gas, Inc. 85 Bodwell Street Avon, Ma developed, which allows EDA determined by testing to be used across the product line. ABSTRACTS GE contracted Kalsi Engineering, Inc. (KEI) to perform actuator testing to determine the effective diaphragm area for the Model 37/38 actuator line and to develop a bounding effective diaphragm area tolerance to account for measurement uncertainties and manufacturing tolerances. The GE sponsored test matrix includes Model 37/38 Sizes 9, 11, 13, 15, 18, and 24 actuators. The test matrix was primary defined to provide EDA data for actuators used in US nuclear power plants. The test matrix was primarily designed to facilitate the evaluation of the effects of stroke position, pressure, diaphragm materials, and measurement uncertainty. The test matrix also included with and without spring test configurations, two spring options for the same actuator size and model, and two diaphragm materials: Nitrile Elastomer and Silicone. The test program provides reliable data for AOV design basis evaluations as required by the NRC RIS This paper presents the results for the Masoneilan Model 38 Size 11 diaphragm actuator, which show that EDA is strongly position dependent and weakly pressure-dependent. As part of the project, a method for determining the required EDA tolerance to account for manufacturing variations was INTRODUCTION Effective Diaphragm Area (EDA) is a primary input for determining the output capability of Air Operated Valve (AOV) Actuators. Potential non-conservatism in EDA for AOV actuators was identified as a key issue by the NRC in 1996 [2], the EPRI AOV Evaluation Guide [3] and the Duke Engineering Report sponsored by the Joint Owner s Group AOV program [4]. Because of the noted importance in EDA values, KEI performed a pilot test program [1]. The GE sponsored test program was built on an original pilot program initiated by Kalsi Engineering, Inc.. NOMENCLATURE = Bias/systematic uncertainty B deff = Effective diaphragm diameter, (in) dc Clamping diameter, (in) dp Diaphragm plate diameter, (in) EDA = Effective diaphragm area, (in2) Ffric = Actuator friction force, (lbf) 1 Published with permission.

2 F m = Measured thrust, (lbf) F spring = Spring force, (lbf) H Diaphragm height (or depth of dish-feature), (in) h 1 Offset between = -1 and y =0, (in) P d = Diaphragm pressure, (psi) S = Random/Precision error t = Student s t-value u = Total uncertainty y Stem position y measured from fail position, (in) Λ Combined product of the weight factor and dimensional tolerance of key parameter in the calculation for EDA tolerance to account for manufacturing tolerances Subscripts EDA = Uncertainty in effective diaphragm area F M = Uncertainty in measured force = Uncertainty in diaphragm pressure P d BACKGROUND Diaphragm actuators are typically single acting; i.e., the actuator is actuated in a single direction via air pressure, and the actuator relies on a spring to return the actuator stem to the fail position. Diaphragm actuators are further categorized by defining the actuator action. Actuator actions are direct-acting or reverse-acting. The actuator stem of a direct-acting actuator extends when the actuator is pressurized (Fig. 1a). The actuator stem of a reverse-acting actuator retracts when the actuator is pressurized (Fig. 1b). The results presented in this paper are for a Masoneilan Model 38 Size 11 diaphragm actuator, which is reverse-acting. The Masoneilan Model 38 actuator is comprised of the same type of primary components as a typical diaphragm actuator (Fig. 2). The most relevant actuator components to this study are the diaphragm, diaphragm plate, diaphragm case, spring, and yoke packing. The measured actuator output force (F m ) consists of the components defined in Equation (1) where EDA is dependent on both pressure and position and the spring force (F spring ) is dependent on position. (1) The diaphragm reacts against the diaphragm plate and case similar to a suspended cable carrying a distributed load. The diaphragm transmits part of the load to the diaphragm case and part to the diaphragm plate. The proportions of the load distribution depend on the shape of the diaphragm which is largely determined by the position of the diaphragm plate relative to the diaphragm caps (see Fig. 3). The Effective Diaphragm Area (EDA) is the area of the diaphragm that contributes to the actuator output by transferring load to the diaphragm plate. The EDA has a corresponding effective diameter (d eff ). The shape of the diaphragm is similar to a catenary curve, and the effective diameter corresponds to the location of zero slope in the curvature of the diaphragm (see Fig. 3). Air Air a) Direct acting b) Reverse acting Figure 1. (a) Direct- and (b) Reverse-acting actuators Figure 2. Masoneilan Model 38, Size 18, air-to-retract 2 Published with permission.

3 d eff Pressure d eff d eff Pressure Pressure a) Fully extended (Fail position) b) Mid-stroke position c) Fully retracted Figure 3. The EDA and corresponding effective diaphragm diameter (deff) change throughout the stroke due to the available slack generated by the relative distance between the diaphragm plate and the clamped diameter. As illustrated by Fig. 3, the EDA for a dish style diaphragm at the fail position is typically the greatest. At the extreme stem position shown in Fig. 3a, the diaphragm plate pulls the diaphragm taut and thereby pushes the effective diameter toward the diaphragm case. As the diaphragm plate is actuated away from the fail position, the relative distance between the diaphragm plate and the clamping diameter (i.e., the point on the diaphragm that is clamped by the case) decreases. The decrease in distance produces slack in the diaphragm. The slack in the diaphragm causes the effective diameter to move off the clamped diameter toward the half way point between the clamped diameter and the diaphragm plate (Fig. 3b). As the diaphragm plate is actuated to the extreme limit of travel (away from the fail position), the relative distance between the diaphragm plate and case again increases. At the extreme travel position illustrated in (Fig. 3c), the position of the diaphragm plate causes the effective diameter to rest on the edge of the plate minimizing the EDA. In addition to the effect stem position has on EDA, the location of the effective diameter can also be affected by manufacturing tolerances in the diaphragm plate, diaphragm, and case. The effects of manufacturing tolerances are addressed in the GE sponsored testing and discussed later here. TEST FIXTURE & TEST PROCEDURES Test Setup The test fixture is shown as Fig. 4. The test fixture is equipped with a double-acting hydraulic cylinder that provides a reaction force for the actuator. The reaction force (hydraulic pressure) is generated when the movement of the piston tries to discharge hydraulic fluid through a variable resistance. The test fixture is designed to allow multiple actuators to be mounted with minimal changes to the fixture. The data was acquired using a National Instruments (NI) compact data acquisition system (DAS) and sensors. The DAS includes analog inputs, analog outputs, and digital outputs (i.e., relays) modules. The sensors include multiple pressure transducers, multiple force transducers, and a position potentiometer. The pressure transducers are used to measure supply pressure and diaphragm pressure. The force transducers are used to measure the actuator stem force, and the position potentiometer is used to measure stem travel. The hydraulic system was automated to allow the test program to position the hydraulic valves reducing manual setup for each dynamic test and more consistent dynamic tests. Test Matrix The test matrix included static, dynamic, and discrete position tests. Static tests were performed with the actuator decoupled from the hydraulic cylinder. The diaphragm pressure and position were recorded as the diaphragm pressure was increased from 0 psi to the actuator casing pressure rating. Dynamic tests were performed with the actuator coupled to the hydraulic cylinder while maintaining a constant diaphragm pressure and using the hydraulic ram to control actuator position and provide the reaction for the actuator. The diaphragm pressure, position, and reaction force were recorded as the hydraulics allowed the actuator to slowly travel. Discrete position tests were performed with the actuator coupled to the hydraulic cylinder. The hydraulic ram was used to maintain a constant stem position. The diaphragm pressure, position, and reaction force were recorded as the diaphragm pressure was varied from the casing pressure to 0 psi. The discrete position test allows the EDA to be determined solely as a function of pressure, as position remains constant. A single Masoneilan Model 38 Size 11 diaphragm actuator was tested with a new nitrile elastomer diaphragm. 3 Published with permission.

4 a) Front View b) Side View Figure 4. Test Fixture with actuator yoke. Dynamic tests were performed for the Size 11 actuator at 20, 30, 40, 50 and 60 psi. Discrete position tests were performed at key stem positions for pressures ranging for the maximum casing pressure down to 0 psi. Uncertainty Analysis The uncertainty analysis is performed using the RSS (root sum of the squares) method for combining uncertainties using the weight terms calculated by taking the partial differential of the result R with respect to the measurands x 1, x 2,, x n. The general expression of the partial derivative of the result R based on the independent measurands x 1, x 2 is given as Equation (2). δr δx δx δx (2) A simplified example of the measurement uncertainty analysis is provided. For a discrete position test, the position dependency of Equation (1) can be omitted because position is constant for each test set (see Equation (3)). (3) The EDA can then be expressed by Equation (4). (4) The spring force (if a spring is installed) and friction force correspond to the measured force with a diaphragm pressure of 0 psi, and Equation (4) can be rewritten as Equation (5). (5) Applying Equation (2) to Equation (5), where the function R is the equation for EDA and the measured pressure and thrust are the independent variables, the expression for the sensitivity of the EDA to pressure for a discrete position (constant position) test is given as Equation (6). 0 (6) The total uncertainty in the EDA (Equation (7)) is comprised of the systematic/bias uncertainty (B EDA ) and the random/precision uncertainty (S EDA ). The systematic/bias uncertainty is given as Equation (8) and accounts for uncertainty due to instrument accuracy, calibration accuracy, data acquisition accuracy, and data filtering, for example. The random/precision uncertainty is given as Equation (9) and accounts for sources of random error such as instrument repeatability, thermal stability of the apparatus and instrumentation, and repeatability of the experiment. The Student s t-value based on the EDA test setup and matrix is dependent on the desired confidence (95%) and 4 Published with permission.

5 the number of degrees of freedom: 4 degrees of freedom exist because 5 tests were conducted at each position. u B ts (7) 2 (8) = 2 (9) Note that in Equation (6) the uncertainty due to the force measurement appears twice as two force measurements are subtracted in Equation (5); the presence of the two force terms requires doubling the uncertainty due to the force measurement in the summation of the systematic/bias uncertainty in Equations (8) and (9). TEST RESULTS The nominal calculated EDA values based on dynamic stroke are provided as Figure 5. The dynamic stroke test and discrete position tests provide nearly identical results. Dynamic stroke tests provide efficient means of studying the effect of position while the discrete position tests provide efficient means of studying the effects of pressure. Agreement between the two test methods indicates that the ramp time used for varying position during the dynamic tests and pressure during the discrete position tests was sufficiently long to ensure a quasi-steady state existed. Agreement between the two test methods also indicates that time/position history does not have a significant effect on the EDA. The dynamic stroke test results show the following: The EDA is largest at the fail position. The rate of change in the EDA (with respect to stem position) initially decreases as the actuator moves away from the fail position and is less sensitive to changes in position in the mid-stroke region. The rate of change in the EDA (with respect to stem position) increases as the actuator approaches the end of travel (fully retracted position) at which point the EDA reaches a minimum value. The discrete position test results for 0.0 inch and 1.0 inches coupled stem position are shown as Figure 6 and Figure 7. The results of the measurement uncertainty analysis are also provided in Figure 6 and Figure 7. The error bars about the EDA values indicate uncertainty in the calculated EDA due to measurement uncertainty. ACCOUNTING FOR MANUFACTURING TOLERANCES Variations in manufactured components exists due to their respective defined dimensional tolerances and the associated manufacturing processes. Variations in key actuator components affect the EDA with respect to position. A methodology was developed to calculate an EDA tolerance based on dimensional tolerances for each actuator size to ensure the bounding EDA values remain conservative. The required EDA tolerance to account for manufacturing tolerances is calculated from Equation (10) weda (10) H dc Tolerance contributions due to the independent parameters (represented by the Λ terms) are determined using weight terms and corresponding dimensional tolerances for the key positions. The weight terms (built into the Λ terms) are derived using a sensitivity equation derived from a dimensionless analysis of the for EDA. The Λ terms are linked to their corresponding independent parameter (H, d c, d p, y and h 1 ) based on the subscript. The contribution of these key parameters to the tolerance is provided as Figure 8. The underlying principle of the methodology is that each key component essentially affects the EDA value with respect to stem position. As such, the methodology consists of a weight factor and the uncertainty in the parameter based on the dimensional tolerances. The weight factor accounts for the effect the parameter has on the EDA and its relationship with position. CONCLUSIONS Based on the results from dynamic and discrete position testing the following conclusions are made: For the actuator studied, the EDA is position and pressuredependent. The sensitivity to changes in position varies based on the distance between the diaphragm support point on the diaphragm plate and the diaphragm clamped point between the diaphragm case halves. Pressure affects the EDA via changing the effective diameter; therefore, over the region of travel in which the EDA is more position sensitive, the EDA will also be more sensitive to pressure. An acceptable EDA value and tolerance must account for variations in manufacturing of the diaphragm case, diaphragm plate, and diaphragm. In low margin applications, measuring the output force (instead of diaphragm pressure) under design basis conditions may be required due to the relatively large tolerance required to bound the uncertainty due to manufacturing tolerances and repeatability. Determining EDA values based on static stroke tests can result in non-conservative values. EDA values should be consistent with the pressure at which the actuator output capability evaluation is to be performed. An uncertainty analysis is required to determine true changes in EDA and apparent changes due to measurement accuracy. dp y h1 5 Published with permission.

6 Effective Diaphragm Area, in 2 Diaphragm Pressure = 20 psi Diaphragm Pressure = 30 psi Diaphragm Pressure = 40 psi Diaphragm Pressure = 50 psi Diaphragm Pressure = 60 psi Stem Position (coupled), in Figure 5. The results of the dynamic tests at 20, 30, 40, 50, and 60 psi Effective Diaphragm Area, in 2 Test #1 Test #2 Test #3 Test #4 Test # Diaphragm Pressure, psi Figure 6. Discrete test results for a coupled stem position of 0-inches with measurement uncertainty indicated by error bars. 6 Published with permission.

7 Effective Diaphragm Area, in Diaphragm Pressure, psi Test #1 Test #2 Test #3 Test #4 Test #5 Figure 7. Discrete test results for a coupled stem position of 1.0-inches with measurement uncertainty indicated by error bars. Contribution to EDA Uncertainty, in 2 Λ H Λ d_c Λ d_p Λ y Λ h_ Coupled Stem Position, inches Figure 8. Contribution of key actuator parameters to account for manufacturing tolerances. 7 Published with permission.

8 REFERENCES 1. Leutwyler, Z., Thidavanh, L., Estep, N., Effective Diaphragm Area Test Program for Air Operated Valve Actuators, Proceedings ASME/NRC Twelfth Symposium, June 2014 Maryland, NRC NRC Information Notice 96-68: Incorrect Effective Diaphragm Area Values in Vendor Manual Result in Potential Failure of Pneumatic Diaphragm Actuators, December Air-Operated Valve Evaluation Guide, EPRI TR , May Effective Diaphragm Area, JOG-TD-03, Duke Engineering & Services, December Masoneilan Evaluation: 12-04, 10 CFR Part 21 Communication, December 4, Wheeler, A. J. and Ganji, A. R., Introduction to Engineering Experimentation, Prentice Hall, New Jersey, Castrup, H. Estimating and Combining Uncertainties, 8th Annual ITEA Instrumentation Workshop, May 5, Test Uncertainty, ASME PTC , ASME, New York, Data Acquisition Systems, ASME PTC , ASME, New York, Published with permission.